1. Field of the Invention
The present invention relates to a method and apparatus for adjusting tracking error balance, which is a reference DC level for a tracking error signal, in an optical disk reproducing apparatus during data reproduction.
2. Description of the Related Art
Optical disks capable of storing large amounts of high-quality digital video/audio data have been widely used. A disk servo system is an essential element required for reproducing data recorded on such an optical disk.
FIG. 1 illustrates a brief schematic diagram of a servo system required for a disk recorder or a disk player. The servo system comprises an optical pickup 10 for reading optical signals from an optical disk 100, a focus error detector 11 for generating a focus error (FE) signal from the signal provided by the optical pickup 10, a tracking error detector 12 for generating a tracking error (TE) signal from the signal provided by the optical pickup 10, a servo controller 13 for creating control signals based on the focus error and tracking error signals, and an actuator driver 14 for moving an objective lens (OL) installed inside the optical pickup 10 in accordance with the control signals.
If the optical disk 100 (e.g., CD or DVD) is loaded into the disk player, the servo system moves the optical pickup 10 toward a predetermined position, i.e., the innermost track 201 on the disk 100 as shown in FIG. 2A. The servo controller 13 then moves the objective lens slowly toward the disk surface to find out when to activate the focus servo. The focus servo is activated when a zero crossing of the focus error signal generated by the focus error detector 11 occurs.
After activating the focus servo, the servo controller 13 measures the peak (TE Peak) and bottom (TE Bottom) values of the tracking error signal generated by the tracking error detector 12 while tracking servo is deactivated. The mean (average) of the peak and bottom values (i.e., (TE Peak+TE Bottom)/2) is set permanently as the tracking error balance and then the tracking servo is activated.
This tracking error balance (TE_balance) is then used as an offset to the tracking error signal throughout all the reproduction operations of the optical disk 100. In other words, as shown in FIGS. 2A and 2B, the tracking error detector 12 subtracts using a subtractor 202 the offset (TE_balance) from the difference (E−F) between E and F signals generated by photodiodes (PD) and passes the result through a filter to produce a tracking drive signal TDO, thereby compensating for errors occurring due to a variation in the property of the disk or optical pickup.
The aforementioned method uses the same tracking error balance measured at the innermost track throughout all the data reproduction operations of the disk. Such one fixed tracking error balance, however, may not be appropriate for outer tracks and may act as a disturbance to the tracking error signal. If the disk is skewed or bent as shown in FIG. 2B, the use of such fixed tracking error balance is especially inappropriate because the bent property of the disk changes the amount of offset balance needed to provide an effective and accurate data reproduction operation.